Agricultural implement



Oct 15, 1963 R. w. BUSHMEYER ETAL AGRICULTURALIMPLEMENT 3 Sheets-Sheet 1Original Filed Aug. 9, 1957 06b 1963 R. w. BUSHMEYER ETAL 3,106,971

mmunm IMP? Original Filed Aug. 9, 195? v 3 sheets sheat a 15, 1953 R. w.BUSHMEYER ETAL 3,106,971

AGRICULTURAL BIPLHIEN'T Original Filed Aug. 9, 1957 1 v 3 Sheets-Sheet 3United States Patent Office 3, l d ,9? l Patented Get. 1 5, l 9633,106,971 AGRICULTURAL IMPLEMENT Richard W. llushmeyer and Clarence E.Henson, Jr.,

Rockford, Ill., assignors to J. 1. Case Company, a corporation ofWisconsin Griginal application Aug. 9, i957, Ser. No. 677,368, newFatent No. 2399,5592, dated .l'uly 4, 1961. Divided and this applicationGet. 28, 1960, Ser. No. 65,733 4 Claims. (-Cl. 172-386) This inventionrelates generally to agricultural implements and is more particularlydirected to improvements in tractor drawn plows, being a division ofprior application, Serial Number 677,368, filed August 9, 1957, nowPatent No. 2,990,892.

In the design and construction of earth-working implements, such asplows, there is usually provided means for adjusting the depth ofpenetration of the earth-working tool. In wheel supported implements,which are adapted to be drawn by a vehicle such as a tractor, it is alsonecessary to provide for vertical adjustment between the frame and thesupporting wheel structure, in order to be able to move the toolssupported on the frame between an elevated position of transport and alowered, ground working position. Various adjusting means have beendevised heretofore, which have attempted to correlate the two mentionedadjustments.

Furthermore, the above-mentioned problem of uniform ground clearance isparticularly troublesome with relatively long ground-working implements,such as multiple-bottom plows, wherein the clearance provided for theplow bottoms in their transport position is dependent to a substantialextent upon the vertical adjustment provided for the implement at pointsspaced in a lengthwise direction. In a multiple-bottom plow there isusually provided a three wheel support, comprising a land wheel, aforward furrow wheel and a rearward furrow or tail wheel. While theadjustment of the land and forward furrow wheels raises and lowers theplow bottoms, some adjustment must also be provided for the rear furrowwheel, if the clearance provided for the several plow bottoms is to besubstantially uniform and the plow is to be transported in asubstantially level position. Consequently, any effective means forraising and lowering the plow bottoms should include a suitablecorresponding adjustment for the vertical position of the rear furrowwheel.

It is the principal object of this invention to provide means forvertically adjusting a wheel-supported, earthworking implement.

it is also an object of this invention to provide improved means forvertically adjusting and positioning the rear or tail wheel of a tractordrawn plow, including novel means for locking such rear wheel inposition for plowing operations. Other objects and advantages will beapparent from the following description of a selected embodiment of theinvention, as seen in the accompanying drawings, wherein:

FIGURE 1 is a perspective view of a multiple-bottom tractor-drawn plow.

FiGURE 2 is an enlarged elevational view, in perspective, of the liftmechanism for the plow.

FIGURE 3 is an enlarged fragmentary view, in perspective, of the rearwheel structure.

FIGURE 4 is an enlarged elevational view of a portion of the structureseen in FIGURE 3.

With reference :to FlGURE 1, it will be seen that the selectedembodiment is a tractor-drawn, five-bottom plow including a framestructure it a forward furrow wheel "12 supported on the frame by acrank axle 14 so as to afford swinging movement of the furrow wheelrelative to the frame, a land wheel 16 also swingably mounted on asecond crank axle 18, a rear furrow wheel or tall wheel structure 2i anda series of moldboard plows 22 fixed to the frame.

More particularly, it will be noted that the plow frame 19 comprises aplurality of plow beams 24a, 24b, 24c, 24d and 24e, which are disposedin generally parallel and laterally spaced positions on the frame, arear frame member 26 which rigidly joins the rearward ends of the plowbeams in staggered relation to each other, preferably through the use ofbolted connections between the frame members and the plow beams, and aforward frame member 28 which rigidly joins the front ends of the plowbeams on the four forwardmost plows. The use of the fabricated beams 26and 28 provides a very rigid construction, and additional bracing may bereadily and inexpensively provided between intermediate portions of theseveral plow beams, as by the brace members 32.

Suitable means is provided at the forward end of the plow structure forcoupling the latter with a tractor or other pulling unit. Preferably,the hitch mechanism includes a cross bar 33 which is pivotally connectedwith each of the four forwardly extending plow beams, and a draw barstructure 34 extends forwardly from this cross bar in position forattachment with a tractor drawbar or the like.

Referring now particularly to FIGURE 2, it is seen that the liftmechanism provided for the plow comprises a lifting clutch 36 which iscarried by the crank axle 13 and is connected with the land Wheel 16 foroperation thereby in a known manner to provide for lifting of the plowin response to rotation of the wheel 16. The lift clutch 36 includes atrip lever 38 which is operable from a position on the tractor. When theclutch is connected in driven relation with wheel 16, the rotation ofwheel 16 effects a corresponding swinging movement of a crank arm 40which is disposed adjacent the inner side of the land wheel. As will beseen hereinafter, this rotation of the crank arm 46 is effective toswing the crank axle 18 relatively to the plow frame and thereby raiseand lower the plow frame relatively to the ground.

The crank axle 18 for the land wheel 16 is suitably rotatably mounted onthe plow frame, as by a plurality of bearing brackets 42, and this crankaxle has fixed thereto, in forwardly extending relation, an arm orbracket 44- which is connected at its free end with the depth adjustingmeans for the plow, indicated generally at 46 in FIGURE 2. Moreparticularly, the depth adjusting means 45 comprises an adjustingquadrant 43 having an arcuate portion including a series of notches 5ttherein, and an adjusting lever 52. The lever 52 is pivotally mounted onthe quadrant 48, as by a bolt 53, for swinging movement relativethereto, and this lever also includes a pin 54 or the like in positionfor selective engagement with one of the notches 59 on the quadrant. Theforward portion of the quadrant 48 is pivotally connected to the plowframe by means of the link 55. One end of the link 56 is pivoted on thequadrant, through means of a bolt 57, and the other end of this link ispivotally connected to a bracket fixed on the beam 24d, as by a pin 58.A rearward portion of the adjusting quadrant is pivotally connected withthe crank axle l8, through a lower end portion 52a of the lever 52, asby the bolt 59. Thus it is seen that the adjusting quadrant 48 issupported on the plow by a double-pivot toggle linkage, referred toherein as a double-toggle linkage, so that the adjusting quadrant 48 ismovable longitudinally of the plow frame as well as vertically withrespect to the frame. The adjusting quadrant is also pivotally connectedto the crank arm 4% on the lifting clutch 36 by means of a lift link 60.This lift link 69 has its lower end pivotally connected to the outer endportion of the crank arm 40 on the lift clutch, as by a pin 61, and theupper end portion of the lift link 50 is pivotally connected to thequadrant 48, as by a pin 62, at a position intermediate the twosupporting pivots 58 and 59 for the quadrant.

As a result of the movement thus afforded for the various members of thelift linkage 46, the plow bottoms 22 are raised, by operation of clutch36, to substantially the same elevation with respect to the ground lineeven though the plows are adjusted for widely varying working depths.

In the preferred embodiment of the invention, wherein the clutch 36 is aknown type generally referred to as a half-revolution clutch, thepositions of engagement for the clutch are disposed so that about 220degrees of clutch rotation is utilized on the lift portion of the cycleand about 140 degrees of clutch rotation is used for the loweringportion of the clutch operation.

It is seen, therefore, that the operation of the clutch 35 during thelift cycle effects a substantially constant height of the plow framerelative to the ground, irrespective of the position of the adjustinglever 52.

As the land wheel-supporting axle 18 is swung relative to the plow frameto provide the described raising and lowering of the plow bottoms,proportional movement is provided for the forward furrow wheel 12,through means including an arm 70 fixed on the crank axle 18 and a link'72 pivotally interconnecting this arm with a bracket 74- FIGURE 1, onthe crank axle 14 for the front furrow wheel. Suitable adjustment isprovided for the front furrow wheel 12 independently of the adjustmentof the land wheel 16, by means of the lever and quadrant arrangement 76.The adjustment thus afforded for the front furrow wheel 12 is for knownpurposes, such as leveling the plow during the breaking of ground etc.

In an elongated implement structure, such as the illustrated five-bottomplow, it is also important to attend to the leveling of the machine in alongitudinal direction, in order to afford trash clearance for the plowin its transport position as well as to provide a proper. and uniformdisposition of the plow bottoms during all phases of the plowingoperation. In the illustrated embodiment, this is provided for by therear wheel structure 20, which is adjustably connected with the abovedescribed lift mechanism 46 for vertical adjustment in response to thevertical adjustment of the forward wheels on the plow.

As seen particularly in FIGURE 3, the rear wheel structure 29 comprisesa wheel 80 which is rotatably mounted on a rearwardly extending endportion of a generally vertical spindle or axle 82. The upper portion ofthis spindle S2 is rotatably received within a cylindrical housingmember 84 and is adjustably held against axial movement relative theretoin a manner which will appear, a set screw 86 extending through thehousing into engagement with the spindle for locking the same againstturning under special conditions. The rearward side of the spindlehousing 84 includes a pair of transversely disposed, spaced-apartbearing members 88, which provide means for supporting the housing atthe rear of the plow in vertically movable relation thereto. Moreparticularly, each of the bearing members 88 has journaled therein oneleg portion of a pair of U-shaped members 99 which extend forwardly ingenerally parallel relation, and which have the other leg portionsthereof journaled in openings provided in a pair of spaced-apart plates92 bolted or otherwise mounted on the rear portion of the plow beam 24a.The free ends of the leg portions of the U-shaped members 99 projectbeyond the bearings 38 and the plate 92 to provide a pivotal support fora lower link 94 and an upper link 96, which complete the double parallellink support for the spindle housing 84.

The upper supporting link 96 has an upwardly turned portion at itsforward end which provides a crank for raising and lowering the parallellinkage and the spindle housing supported thereby. More particularly, abell crank 93 is pivotally mounted, through a pin 100, supported fromthe adjoining plate 92, and the rearward end of this bell crank ispivotally connected to the crank portion of the upper link 96 through alink 102. A forwardly and upwardly extending portion of the bell crank98 also includes a pin 194 affording pivotal connection with the rearendof an adjusting rod 106 for the rear wheel structure. As seen in FIGURES1 and 2, the adjusting rod 106 extends forwardly on the plow structureand has its forward end slidably disposed'in a collar 1118 FIGURE 2,which is pivotally supported in a yoke 119 fixed to the upper end of abracekt 112. The bracket 112 is bolted to the arm 44 for movementtherewith upon rotation of the crank axle 18. A nut 114 which isadjustably threaded on the end of rod 196 prevents withdrawal of the rodfrom its collar 108, and a coil spring 116 is disposed around the rod106 between the collar 108 and a pin 118 to afford yielding movement ofthe rod in a forward direction.

Thus it is seen that the rear Wheel structure 20 will be raised andlowered in response to operation of the clutch 36 on the land wheel 16,through rotation of the arm 44 and the accompanying longitudinalshifting of the rod 106. The vertical movement thus afforded for therear wheel structure is correlated with the operation of the liftlinkage 46, so that the plow bottoms are essentially leveled lengthwiseof the plow when the latter is in its transport and plowing positions.Furthermore, it will be noted that, with the spring 116 positioned asdescribed, the adjusting rod 166 is permitted to move forwardlysufficiently to absorb any shock that might be imparted to the rearwheel, and to allow the tail wheel to drop to stay in the furrow if theframe 10 is raised by an obstruction.

With the use of a rear furrow or tail wheel, such as wheel 89, it isimportant that the rear wheel be free to caster during the turning ofthe plow, but that this wheel be held in a generally straight path oftravel during the plowing operation. In the illustrated embodiment, therear wheel 81) is locked in position to follow the direction of travelof the plow by novel means including cooperating locking elementscarried by the rear wheel and by the plow frame structure, respectively.

The structure provided for thus controlling the rear Wheel includes agenerally cylindrical cam member 120 FIGURE 3, which is disposed at thetop of the spindle housing 84 and is fixed to the spindle 82 forrotation therewith by a clamping element 122 and normally fixed, whenthe plow is plowing, in relation to the plow frame or specifically inrelation to plates 92. A central portion of the clamp 122 includes a key124 which engages a longitudinal groove 125 on the upper end of thespindle to thereby provide for rotation of member 12% and the spindle 82together. The clamp 122 is detachably fixed to the cylindrical member bya pair of bolts 123 which extend through laterally extending earportions on the clamp and through lugs projecting outwardly fromopposite sides of member 120 in fixed relation thereto.

It is necessary to be able to adjust tail wheel 81 toward the right orleft in order to make it take over the side thrust resulting from thewell-known tendency of the plow bottoms to cut too far sidewise into theunplowed land and this is accomplished by clamp 122. As clearly shown inFIGURE 3, said ear portions have curved surfaces 128 and 123, againstwhich bear nuts 128 and 128 respectively, so that the nuts may seatproperly with clamp 122 in various adjusted positions, shifting of theclamp being possible by reason of the normal clearance of the openingsin the clamp about 'bolts 128. With nuts 128 and 12% tight, spindle 82will be rigidly clamped to member 1253, while loosening one nutslightly, and tightening the other, will turn clamp 122 and, by virtueof the keyed connection 124, spindle 82. This will turn or adjustspindle 82 in relation to member 120', and therefore in relation to theplow frame, as will appear.

The lower edge portion of the cylindrical member 121] includes anarcuate, flanged portion 132 (see also FIG- URE 4) which extendsapproximately half way around the cylinder and includes an inwardlyfacing groove for receiving a circumferential rim 134 on the upper endof the spindle housing 84. The member 12 is free to rotate relatively tothe spindle housing, but is held against axial displacement relativethereto by interengagement of rim 1% and the groove in flange 132, a setscrew 136 extend ing through the flange 32 to a position underlying therim 134 to prevent rotation of member 12% when desired. The upper end ofthe spindle housing 84 also includes, at its rear side, a rib 138 whichprovides, at either edge thereof, a stop in position to engage one endof flange 132. and thereby limit the rotation of the cylindrical member12%) and the spindle 82 fixed thereto. In this way, the amount ofcastering provided for the rear Wheel 8% is controlled. Further, thereis provided a set screw 1% which is threaded through the top of themember 120, and the adjustment of this screw is effective when clamp 122is loosened to position the spindle 82 vertically with respect to itshousing 34 This will provide the limited vertical adjustment of the tailWheel necessary under varying conditions.

The outside surface of the cylinder 12%) also includes a curving flangesurface or cam track 142, seen particularly in FIGURE 4, which facesforwardly on the plow and is adapted for engagement by a tapered roller1%. More particularly, roller 144 is frusto-conical in shape and isdisposed so that the apex of its cone is virtually at the center axis ofthe spindle 82 during engagement of the curved surface 142 on thecylinder 12%. The roller 14 is rotatably mounted on a shaft portion of abracket 1 36 which is detachably fixed in position between plate members92. The bracket 146 also includes a cylindrical hearing or boss portionat one side for receiving the hereinbefore-mentioned pin 3"3 supportingthe bell crank 9-3.

The curving surface 142 is arranged generally helically about member3.23 and is designed for cooperation with the conical roller 14-!- in amanner such that the tangential velocity of any point on the rollerabout its axis is equal to the tangential velocity of a coincident pointon surface 142 about the vertical axis of spindle 82, along substandailythe entire length of the curved portion of surface As a result,engagement of roller 1 54 with surface 142. during lowering movement ofthe plow produces a pure rolling motion for the roller 144. This notonly provides for less wearing of these parts, but also enables thewheel locking mechanism to perform more smoothly and in less time thanother known arrangements.

Engagement of the conical roller 144 with the curving surface 142 is, ofcourse, effective to lock the tail wheel axle 82 against rotation withinits housing 34 when the plows are lowered. This is necessary so thatwhen the plows are in the ground, the tail wheel 89 is locked so thatits direction of travel is generally parallel to the direction of travelof the plow structure. However, when the plows are raised out of theground it is desirable that the tail wheel be free to caster, asrequired in turning the plow in preparation for entering a new furrow.As seen in FIGURE 3, the plows are in transport position and the conicalroller 144 has been moved completely out of engagement with the curvedsurface 142 so that the tail wheel Elli is free to caster.

When the plow is dropped, that is the plow bottoms are lowered into theground, through operation of clutch 36 and linkage an, the rear tailwheel 89 is moved upwardly by virtue of the connection between rod 195and the lift mechanism 46. As the rear wheel structure moves upwardly,the conical roller 144 engages the curved surface 1422. Assuming theplow has been turning in preparation for opening a new furrow, the wheelso will be turned so that the roller 44 engages one of the upper edgesof the surface 142, as indicated in FIGURE 4 at 144a and 14412,depending upon the direction in which wheel 39 is turned. Of course, ifthe tail wheel 89 is already in line with the direction of travel of theplow, the conical roller 144 will move directly into the bottom or Ushaped portion of the curved surface 142, as indicated at 1440' inFIGURE 4, which position is the normal plowing position, and wherein thedownward pressure of the plow frame during operation is imposed uponcylinder and thence upon wheel 86.

By virtue of the described relationship between the roller 144- andsurface 142, as the roller engages one of the upwardly facing edgesurfaces of the curving member 142., it will roll along this surface anddown the side wall thereof into the centered locking position, indicatedas position 144C for the roller. In this respect, it will be noted that,in the selected embodiment, one of the side wall portions 142a ofsurface 142 is substantially higher than the opposite side wall 142i:and includes a generally straight portion. This design is for thepurpose of providing greater stability for the rear wheel, against thenormal lateral thrust on this wheel during plowing. Unless there issufiicient depth given to the curved surface 142 there may be a tendencyfor the conical roller 144 to jump out of its locked position and permitthe tail wheel to caster. This is undesirable and, consequently, thelong straight wall portion 1420 has been placed on the side in thedirection of the lateral thrust normally placed on the plow structure.Another reason for the use of one generally straight side along thecurving surface 142 is to better maintain the tail wheel 3:? in positionwhen the plow bottoms strike an object and the entire structure israised vertically. When this occurs, the momentary raising of the roller144 will not immediately result in a release of the wheel, as the normallateral thrust on the tail wheel will hold the roller against thestraight portion of wall 142a. and the roller will then drop back intoits locking position seen at 1440, such motion of wheel 8% beingaccommodated by a compressing of spring 1H5.

Moreover, with the illustrated design for the curving surface 1 52 thereis advantage in connection with moving the plows into their soil workingposition. If in moving into position, the plow is making a right turn,the roller 144 will initially engage the upwardly facing edge portion ofthe higher wall portion 142a. Consequently, the rear end of the plowwill be maintained in a higher position somewhat longer as the plow isbeing directed into position, and the plow points will be tilteddownwardly to allow them to pierce the ground before the roller 144rnoves downwardly along surface 142 and the tail wheel is actuallylocked in its plowing position. This is very desirable because, whencoming out of the right hand turn, the ground forces against the plowbottoms are the greatest and considerable guidance and stability isrequired for the plow in this circumstance. When coming out of a lefthand turn and the plows are entering the ground, the plow bottoms areslicing into the ground and the forces are considerably less than in thecase of the right hand turn where considerable pressure is being exertedagainst the landsides of the plows. Under the left turn conditions, asthe plows are dropped, roller 144 contacts surface 142b and promptlyturns cylinder 120 into working position designated as 1440. Sinceportion 142!) is active only while the plow is coming out of a leftturn, it does not need a long vertical wall as 142a, and is given asharp slant to facilitate such turning action.

The above described adjustments afforded for the land wheel 16, thefurrow wheel 12 and the tail wheel 86 correlate the vertical movement ofthe three wheels, so that in entering or leaving the soil the plowbottoms are essentially level with the ground. This is particularlyimportant in connection with breaking ground. It is important that eachof the plow bottoms enter the ground at essentially the same time and atthe same angle with respect to the ground, if maximum efiiciency is tobe achieved.

It is seen from the vforegoing, therefore, that there is provided anovel arrangement for locking the tail wheel in position during plowing,which arrangement is particularly advantageous in that it eliminatesessentially all friction between the locking components during thenecessary relative movement therebetween. The described lockingarrangement for the tail wheel is also advantageous in that it preventsinadvertent release of the tail wheel, as by the plow striking anobject, and operates particularly effectively to control the wheelduring turning movement of the plow, so that the rear of the plow isheld elevated until the bottoms are properly positioned to enter theground and the rear wheel is then securely locked in position.

Although shown and described with respect to particular structure, itwill be apparent that the disclosed construction is subject tomodifications apparent to those skilled in the art without departingfrom the principles of this invention.

We claim:

1. In a wheel-supported ground-working agricultural implement includinga tool supporting frame, a rear wheel structure comprising a pair ofparallel links pivotally mounted at one end on said supporting frame, aspindle housing carried by the free end portion of said parallel links,a spindle rotatably disposed within said housing and including arearwardly extending lower portion mounting a rear wheel thereon, meansfor moving said housing vertically relative to said frame, and means forlocking said spindle and rear wheel in position with respect to saidframe to provide a straight path of movement for said rear wheel, saidlocking means comprising a cam member carried at the upper end of saidspindle in fixed relation thereto, said cam member including a generallyupwardly facing curving surface including a pair of side wall portionsand a lower center portion, and a conical roller member rotatablymounted on said frame in position for engagement with said curvingsurface, said curving surface being shaped to contact said conicalroller throughout the length thereof and having a portion disposedgenerally helically about said cam member, whereby vertical movement ofsaid wheel structure and said cam member is effective to provide forengagement of said conical roller with said curving surface and saidroller is movable along said curving surface to said lower centerportion thereof to thereby swing the rear wheel and lock it in positionwith respect to said frame.

2. A control for the tail wheel on a plow of the type having a wheelcarried frame adapted to be raised and lowered and a tail wheel havingan axle including an upwardly directed spindle portion, the combinationof a housing member in which said spindle portion is ournaled forrotating movement for castering action of the tail wheel, means forraising and lowering said frame relatively to said housing member, a cammember fixed in rela tion to said spindle portion and providing a camtrack, a tapered roller journaled on the frame in position to contactthe cam track for controlling said castering action as the frame islowered, the cam track being shaped to be contiguous with the taperedroller in all positions of contact therewith, said cam track having anupper portion arranged generally helically about said spindle portion,merging into a downwardly directed substantially straight guidingportion generally parallel to the axis of said spindle, and a lowerportion of upwardly open U shape contoured to fit about the taperedroller, said cam track continuing upwardly on the other side of saidlower portion generally helically about said spindle.

3. A control for the tail wheel on a plow of the type having a wheelcarried frame adapted to be raised and lowered and a tail wheel havingan axle including an upwardly directed spindle portion, the combinationof a housing member in which said spindle portion is journaled forrotating movement for castering action of the tail wheel, means forraising and lowering said frame relatively to said housing member, a cammember fixed in relation to said spindle portion and providing a camtrack, a tapered roller journaled on the frame in position to contactthe cam track for controlling said castering action as the frame islowered, the cam track being shaped to be contiguous with the taperedroller in all positions of contact therewith, said cam track having anupper portion arran ed generally helically about said spindle portion,merging into a downwardly directed substantially straight guidingportion generally parallel to the axis of said spindle, and a lowerportion contoured to fit about the tapered roller for locking the tailwheel in non-castering position.

4. A control for the tail wheel on a plow of the type having a wheelcarried frame adapted to be raised and lowered and a tail wheel havingan axle including an upwardly directed spindle portion, the combinationof a housing member in which said spindle portion is journaled forrotating movement for castering action of the tail wheel, means forraising and lowering said frame relatively to said housing member, a cammember fixed in relation to said spindle portion and providing a camtrack, a tapered roller journaled on the frame in position to contactthe cam track for controlling said castering action as the frame islowered, the cam track being shaped to be in contact with the taperedroller throughout its length in all positions of contact therewith, saidcam track having an upper portion arranged generally helically aboutsaid spindle portion for restoring said spindle to straight positionafter a turn in one direction, said upper portion merging into adownwardly directed substantially straight guiding portion generallyparallel to the axis of said spindle for maintaining said straightposition during limited raising movement of the frame, a lower portioncontoured to fit about the tapered roller, and said cam track continuingupwardly on the other side of said lower portion generally helical-1yabout said spindle for restoring said spindle to straight position aftera turn in the other direction.

References Cited in the file of this patent UNITED STATES PATENTS1,865,598 Verity July 5, 1932 2-076.666 Ohlendorf Apr. 13, 1937

1. IN A WHEEL-SUPPORTED GROUND-WORKING AGRICULTURAL IMPLEMENT INCLUDINGA TOOL SUPPORTING FRAME, A REAR WHEEL STRUCTURE COMPRISING A PAIR OFPARALLEL LINKS PIVOTALLY MOUNTED AT ONE END ON SAID SUPPORTING FRAME, ASPINDLE HOUSING CARRIED BY THE FREE END PORTION OF SAID PARALLEL LINKS,A SPINDLE ROTATABLY DISPOSED WITHIN SAID HOUSING AND INCLUDING AREARWARDLY EXTENDING LOWER PORTION MOUNTING A REAR WHEEL THEREON, MEANSFOR MOVING SAID HOUSING VERTICALLY REALTIVE TO SAID FRAME, AND MEANS FORLOCKING SAID SPINDLE AND REAR WHEEL IN POSITION WITH RESPECT TO SAIDFRAME TO PROVIDE A STRAIGHT PATH OF MOVEMENT FOR SAID REAR WHEEL, SAIDLOCKING MEANS COMPRISING A CAM MEMBER CARRIED AT THE UPPER END OF SAIDSPINDLE IN FIXED RELATION THERETO, SAID CAM MEMBER INCLUDING A GENERALLYUPWARDLY FACING CURVING SURFACE INCLUDING A PAIR OF SIDE WALL PORTIONSAND A LOWER CENTER PORTION, AND A CONICAL ROLLER MEMBER ROTATABLYMOUNTED ON SAID FRAME IN POSITION FOR ENGAGEMENT WITH SAID CURVINGSURFACE, SAID CURVING SURFACE BEING SHAPED TO CONTACT SAID CONICALROLLER THROUGHOUT THE LENGTH THEREOF AND HAVING A PORTION DISPOSEDGENERALLY HELICALLY ABOUT SAID CAM MEMBER, WHEREBY VERTICAL MOVEMENT OFSAID WHEEL STRUCTURE AND SAID CAM MEMBER IS EFFECTIVE TO PROVIDE FORENGAGEMENT OF SAID CONICAL ROLLER WITH SAID CURVING SURFACE AND SAIDROLLER IS MOVABLE ALONG SAID CURVING SURFACE TO SAID LOWER CENTERPORTION THEREOF TO THEREBY SWING THE REAR WHEEL AND LOCK IT IN POSITIONWITH RESPECT TO SAID FRAME.